Wood based panels are commonly used in building industry as floor sheathing and flat roof sheathing. When used in these applications, panels are preferably formed with some sort of tongue and groove profile to allow for quick and efficient interlocking of the panels during construction. The panels span the distance between supporting joists with the interlocking tongue and groove side edges of adjacent panels serving to support the panels against deflection between the joists while the end edges of the panels are located over and supported by the joists.
Canadian Patent 914,370 which issued to applicant discloses a tongue and groove profile for a plywood panel suitable for use as a floor or flat roof panel. Patent 914,370 discloses a tongue and groove profile in which the inner walls of the groove are essentially parallel except for the inner most region adjacent the groove base adapted to accommodate the tongue tip. The opening or clearance of the groove is only slightly larger than the thickness of the tip of the tongue. As a result of this arrangement, it can become very difficult to insert the tongue into the groove during the installation process, particularly if the panel edges are slightly wavy or bowed or if the edge profiles are swollen due to an increased moisture content.
U.S. Pat. No. 4,807,416 which also issued to applicant, discloses a tongue and groove profile having a twin wedge configuration that makes the installation of a swollen profile easier. However, as the resulting joint dries out after installation, the tongue will tend to shrink creating play in the joint that leads to differential deflections between the profiled edges of adjacent panels, greater than acceptable for flooring type of panels.
Also, some profiles used in oriented strandboard and waferboard are of a single wedge-like shape and while they make the installation of a swollen profile somewhat easier, the swelling prevents the tongue from reaching the bottom of the groove and after drying out while installed, a large tolerance between the groove and tongue results, and may cause excessive differential deflections between the profiled edges of the adjacent panels, unacceptable or undesirable for flooring applications.